This application is related to and claims priority from Japanese Patent Applications No. Hei. 10-282799 filed on Oct. 5, 1998 and No. Hei. 11-222682 filed on Aug. 5, 1999, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an air conditioning apparatus which adjusts temperature of air blown into a passenger compartment by adjusting an amount of hot water flowing into a heating heat exchanger, while restricting a variation in temperature of blown-air due to a variation in a rotation speed of an engine. The air conditioning apparatus is suitable for a one-box type recreational vehicle (RV), for example.
2. Description of Related Art:
In a vehicle air conditioning apparatus having a rear air-conditioning unit for controlling temperature of air blown toward a rear seat side of a passenger compartment, temperature of air blown into the passenger compartment is controlled by a flow control valve for adjusting an amount of hot water flowing into a heating heat exchanger so that a size of the rear air-conditioning unit is reduced. In the air conditioning apparatus, a water pump driven by an engine of the vehicle is disposed in a water circuit of the engine, and hot water heated by the engine is supplied into the heating heat exchanger by the water pump. Therefore, when a rotation speed of the engine is increased, the amount of hot water flowing into the heating heat exchanger is increased so that the temperature of air blown into the passenger compartment is also increased, even when an opening degree of the flow control valve is set to be equal.
In view of the foregoing problems, it is an object of the present invention to provide an air conditioning apparatus for a vehicle, which can decrease a variation in temperature of air from a heating heat exchanger, due to a variation in a rotation speed of an engine.
According to the present invention, an air conditioning apparatus includes a heating heat exchanger for heating air by performing heat exchange between water in a water circuit and air passing therethrough, and a flow control valve which adjusts a flow amount of water flowing into the heating heat exchanger to adjust temperature of air blown from the heating heat exchanger. The flow control valve includes a water bypass passage through which water bypasses the heating heat exchanger, and a pressure-response valve for adjusting an opening degree of the water bypass passage in accordance with pressure of water supplied from the engine by a water pump which is driven by the engine. In the air conditioning apparatus, an opening degree of the flow control valve is controlled by a control unit to become a target opening degree so that the flow amount of water flowing into the heating heat exchanger is controlled, and the target opening degree of the flow control valve is corrected by a control unit in a direction for reducing variation in the flow amount of water flowing into the heating heat exchanger due to variation in a rotation speed of the engine. Thus, variation in temperature of air blown from the heating heat exchanger due to the variation in the rotation speed of the engine can be reduced, and air-conditioning feeling for a passenger in a passenger compartment of the vehicle can be improved.
Preferably, the control unit corrects the target opening degree of the flow control valve to absorb the variation in the flow amount of water flowing into the heating heat exchanger due to the variation in the rotation speed of the engine, when the target opening degree of the flow control valve is larger than a predetermined degree. Therefore, even when an adjustment of water passing through the water bypass passage due to the pressure-response valve is insufficient when the flow control valve is opened with a high opening degree, the variation in the amount of water flowing into the heating heat exchanger can be sufficiently adsorbed by correcting the target opening degree.
More preferably, the control unit corrects the target opening degree of the flow control valve to increase the target opening degree of the flow control valve by a predetermined degree from a set target value when the rotation speed of the engine is lower than a first predetermined value approximately corresponding to a rotation speed during an engine-idling, and the control unit further corrects the target opening degree so that the target opening degree is reset to the set target value when the rotation speed of the engine is increased to be higher than the first predetermined value. Therefore, even when the engine is operated with a rotation speed approximately corresponding to the rotation speed during the engine idling, it can effectively prevent temperature of air blown from the heating heat exchanger from being decreased.
On the other hand, the control unit corrects the target opening degree of the flow control valve to decrease the target opening degree of the flow control valve by a predetermined degree from a set target value when the rotation speed of the engine is increased to be higher than a second predetermined value which is greatly larger than the first predetermined value, and the control unit further corrects the target opening degree so that the target opening degree is reset to the set target value when the rotation speed of the engine is decreased to be lower than the second predetermined value. Therefore, it can effectively prevent temperature of air blown from the heating heat exchanger from being extremely increased due to an increased water amount when the engine is operated with a high rotation speed.